Single-Coil Pickups
Early electromagnetic pickups, such as U.S. Pat. No. 1,915,858 (Miessner, 1933) could have any number of coils, or one coil, as in U.S. Pat. No. 2,455,575 (Fender & Kaufmann, 1948). The first modern and lasting single-coil pickup design, with a pole for each string surrounded by a single coil, seems to be U.S. Pat. No. 2,557,754 (Morrison, 1951), followed by U.S. Pat. No. 2,968,204 (Fender, 1961). This has been followed by many improvements and variations. In all those designs, starting with Morrison's, the magnetic pole presented to the strings is fixed.
Dual-Coil Humbuckers
Dual-coil humbucking pickups generally have coils of equal matched turns around magnetic pole pieces presenting opposite magnetic polarities towards the strings. Lesti, U.S. Pat. No. 2,026,841, 1936, perhaps the first humbucking pickup, had multiple poles, each with a separate coil. Lover, U.S. Pat. No. 2,896,491, 1959, had a single magnet providing the fields for two sets of poles, one for each string, with a coil around each set, the pickup design which most modern humbuckers use. These have been followed by a great many improvements and variations, including: Fender, U.S. Pat. No. 2,976,755, 1961; Stich, U.S. Pat. No. 3,916,751, 1975; Blucher, U.S. Pat. No. 4,501,185, 1985; and Knapp, U.S. Pat. No. 5,292,998, 1994;
Humbucking Pairs
Nunan, U.S. Pat. No. 4,379,421, 1983, patented a reversible pickup that could present either pole to the strings. But the patent only mentions rotating the middle pickup of three to produce two humbucking pairs with the neck and bridge pickups, using a 5-way switching system. It does not present a humbucking pair made with the neck and bridge pickups. Fender, U.S. Pat. No. 4,581,975, 1986, may be the first to use the term “humbucking pairs” (column 2, line 31), stating in column 2, line 19, “Thus, it is common for electrical musical instruments to have two, four or six pick-ups.” Yet, in the 3-coil arrangement of his patent, with the middle pickup presenting North poles to the strings and the neck and bridge pickups presenting South poles to the strings, he did not combine the signals from those pickups to form humbucking pairs. Instead, he added dummy pickups between them, underneath the pick guard (FIG. 2), without magnetic poles, for provide the hum signals for cancellation.
Commonly manufacture of single-coil pickups are not necessarily matched. Different numbers of turns, different sizes of wires, and different sizes and types of poles and magnets produce differences in both the hum signal and in the relative phases of string signals. On one 3-coil Fender Stratocaster (tm), for example, the middle and neck coils were reasonably similar in construction and could be balanced. But the bridge coil was hotter, having a slightly different structure to provide a stronger signal from the smaller vibration of the strings near the bridge. Thus in one experiment, even balancing the turns as closely as possible produced a signal with phase differences to the other two pickups, due to differences in coil impedance.
A previous patent (U.S. Pat. No. 9,401,134, 2016, Baker), which supports this invention, used the concept of humbucking pairs and switching systems for four single-coil electromagnetic pickups with coils of equal turns. Baker modified standard single-coil pickups, adding turns until four single-coil pickups have a reasonably equal response to external AC fields, and shocked the magnets of two of them, with a stronger rare-earth magnet, to reverse the poles, providing two matched pickups with North poles toward the strings (N-up) and two matched pickups with South poles toward the strings (S-up). Limited to two 4P5T lever switches, that system had no out-of-phase, or contra-phase, humbucking pairs, but four humbucking pairs and one humbucking quad of parallel-connected pickups on one 5-way switch, and four series-connected pairs with a series-parallel connected quad on the other 5-way switch.
The NP patent application Ser. No. 15/616,396 (Baker, 2017), Humbucking switching arrangements and methods for stringed instrument pickups, extended this invention to humbucking quads, hexes, octets and up, as well as the special case of a humbucking triple. It makes clear that that any electronic switching system for electromagnetic sensors must know which pole is up on each pickup in order to achieve humbucking results. The NP patent application Ser. No. 15/917,389 (Baker, 2018), Single-Coil Pickup with Reversible Magnet & Pole Sensor, presented embodiments of single-coil pickups with magnets that could be removed and reversed, providing as well a signal for the state of the reversal.
For two matched pickups, the humbucker connections, either series or parallel, must be contra-phase if they have the same poles up, and in-phase of they have different poles up. For K number of matched pickups, this makes possible K*(K−1)/2 pair combinations, regardless of poles or series-parallel connections. For example, for four matched pickups A, B, C & D, the unique pair combinations are AB, AC, AD, BC, BD and CD, or 4*3/2=6. If they all have the same pole up, i.e., (N,N,N,N), then all the combinations are contra-phase, and moving any pickup to any other position has no effect. If they have one pole different, i.e., (N,S,S,S), then that pole can be moved to 4 different positions. If they have 2 poles different, i.e., (N,N,S,S), then those poles can be placed uniquely only as (N,N,S,S), (N,S,N,S) and (N,S,S,N), since reversing the poles, i.e., (S,S.N,N), (S,N,S,N) and (S,N,N,S) produce exactly the same in-phase and contra-phase humbucking pair combinations. This total 8 different pole configurations. (See also, https://www.researchgate.net/publication/323686205_Making_Guitars_with_Multiple_Tonal_Characters)
It turns out that if the pickup poles are reversible, for K number of pickups, there can be 2K-1 different pole configurations, each configuration producing K*(K−1)/2 humbucking pairs, each configuration producing K*(K−1) potentially unique humbucking tones, if both series and parallel pair connections are considered. But all the pole configuration have some common tones. There can be only 2*K*(K−1) potentially unique humbucking tones from the 2K-1 different pole configurations. For 5 pickups, this is 16 different pole configurations, with 20 potentially unique humbucking pair tones for each configuration, with a total of 40 unique humbucking pair tones for the entire set. For K>7, the number of pole configurations exceeds the number of potentially unique tones.
Even for just humbucking pairs, never mind triples, quads, quintets and hextets, it would be a challenging problem for either electro-mechanical or digitally-controlled pickup switching systems to take full advantage of reversible pickup poles.
Electro-Mechanical Guitar Pickup Switching
The standard 5-way switch (Gagon & Cox, U.S. Pat. No. 4,545,278, 1985) on an electric guitar with 3 single-coil pickups typically provides to the output: the neck coil, the neck and middle coils in parallel, the middle coil, the middle and bridge coils in parallel, and the bridge coil. Typically, the middle pickup has the opposite pole up from the other two, making the parallel connections at least partially humbucking. But while the middle and neck coils have roughly equal numbers of turns, and the bridge coil has more turns than the other two to produce a roughly equal signal from the smaller physical vibrations of the strings nearer the bridge. The standard 3-way switch on a dual-humbucker guitar typically produces the neck, neck∥bridge and bridge pickups at the output, all of which are humbucking.
These two switches are “standards” because the vast majority of electric guitars on the market use them. There are other switching systems, such as U.S. Pat. No. 3,290,424, Fender, 1966; U.S. Pat. No. 4,305,320, Peavey, 1981; U.S. Pat. No. 5,136,918, Riboloff, 1992; U.S. Pat. No. 5,311,806, Riboloff, 1994; U.S. Pat. No. 5,763,808, Thompson, 1998; U.S. Pat. No. 6,781,050B2, Olvera, et al., 2004; US2005/0150364A1, Krozack, et al.; U.S. Pat. No. 6,998,529B2, Wnorowski, 2006; and US2009/0308233A1, Jacob. But they are either not on the market, or fill niche positions. In any case, they do not intersect or interfere with the switching systems presented here.
Microcontrollers in Guitar Pickup Switching
Ball, et al. (US2012/0024129A1; U.S. Pat. No. 9,196,235, 2015; U.S. Pat. No. 9,640,162, 2017) describe a “Microprocessor” controlling a “digitally controlled analog switching matrix”, presumably one or more solid-state cross-point switches, though that is not explicitly stated, with a wide number of pickups, preamps and controls hung onto those two boxes without much specification as to how the individual parts are connected together to function. According to the Specification, everything, pickups, controls, outputs and displays (if any), passes through the “switching matrix”. If this is comprised of just one cross-point switching chip, this presents the problem of inputs and outputs being interrupted by queries to the controls. In the Specification, the patent cites the ability to make “any combination of combinations” without describing or providing a figure any specific one, or even providing a table or scheme describing the set. It states, “On board controls are similar to or exactly the same as conventional guitar/bass controls.” But there is not enough information in the patent for someone “with ordinary skill in the art” to either construct or fully evaluate the invention.
The Ball patents make no mention or claim of any connections to produce humbucking combinations. The flow chart, as presented, could just as well be describing analog-digital controls for a radio, or record player or MPEG device. In later marketing (https://www.music-man.com/instruments/guitars/the-game-changer), the company has claimed “over 250,000 pickup combinations” without demonstration or proof, implying that it could be done with 5 coils (from 2 dual-coil humbuckers and 1 single-coil pickup).
Baker (NP patent application Ser. No. 15/616,396, 2017) systematically developed series-parallel pickup topologies from 1 to 5 coils, with 6 coils in notes not included. (See also https://www.researchgate.net/publication/323390784_On_the_Topologies_of_Guitar_Pickup_Circuits) The table labeled Math 12b in that application shows that 5 coils can produce 10717 unique circuits of sizes from 1 to 5 coils, including reversals of individual pickup terminals and moving pickups around the circuit positions. Math 12b shows that 6 coils can produce 286,866 unique circuits of from 1 to 6 coils. “Over 250,000” circuits are possible only with 3 humbuckers, or with 5 coils and a piezoelectric pickup.
Bro and Super, U.S. Pat. No. 7,276,657B2, 2007, uses a micro-controller to drive a switch matrix of electro-mechanical relay switches, in preference to solid-state switches. The specification describes 7 switch states for each of 2 dual-coil humbuckers, the coils designated as 1 and 2: 1, 2, 1+2 (meaning connected in series), 1−2 (in series, out-of-phase), 1∥2 (parallel, in-phase), 1∥1(−2) (parallel, out-of-phase), 0 (no connection, null output). In Table 1, the same switch states are applied to 2 humbuckers, designated neck and bridge. That is three 7-way switches, for a total number of combinations of 73=343.
In this arrangement, null outputs occur when a series connection is broken. This will happen once for all 3 switches set to null, and each time a series connection in the last switch is broken by a null output in the previous two switches, for a total of at 5 null outputs. Although Super has argued via unpublished e-mail that a reversed output connection is a separate tone, this inventor calls it a duplicate. This can happen when the 7-way output switch is set to parallel and out-of-phase for the second humbucker, the first humbucker 7-way switch is set to null, and the second humbucker 7-way switch is set to any output, or 6 combinations. Taking out 5 nulls and 6 duplicates that leaves 332 useful combinations.
Table 1 in Bro and Super cites 157 combinations, of which one is labeled a null output. For 4 coils, the table labeled Math 12b in Baker, NP patent application Ser. No. 15/616,396, 2017, identifies 620 different combinations of 4 coils, from 69 distinct circuit topologies containing 1, 2, 3 and 4 coils, including variations due to the reversals of coil terminals and the placement of coils in different positions in a circuit. Baker shows how an all-humbucking 20-combination electromechanical switching circuit for two humbuckers produces mean frequencies for 6 strummed strings which have 3 or 4 duplicate tones, with a tendency for mean frequencies to bunch at the warm end of the scale. The use of mean frequency in this manner has not yet been established as a measure of tone, but as a first approximation still raises the question of the practical use of so many tones so close together.
Baker, NP patent application Ser. No. 15/616,396, 2017, demonstrates, in the table labeled Math 31, that the total number of potentially distinct humbucking tones from topologically different electrical circuits of matched guitar pickups, using just simple series-parallel topologies, can be up to 2 for 2 sensors, 6 for 3, 48 for 4, 200 for 5, 3130 for 6 and 19,222 for 7 sensors, up to 394,452 for 8 sensors. Beyond 3 or 4 matched single-coil pickups, electro-mechanical switches are too expensive and impractical. One must us a cross-point matrix or switch of some kind, preferably analog-digital. Baker offered an architecture for a micro-controller system using a solid-state cross-point switch, specifying how the switch is dedicated to sensors, noting that for Mx/2 number of 2-wire sensors, an Mx by (My=Mx+2) crosspoint switch, or larger, will cover all possible interconnections, and provide a 2-wire output. But for humbucking circuits made of matched single-coil pickups, as disclosed in that NPPA, the orientation of the pickup magnetic poles to the strings must be known by the microcontroller. This requires the pickup poles to be manually assigned in the microcontroller switching or programming, or for the microcontroller to directly detect the orientation of the pickup poles. This programming problem has not yet been solved.